The present invention relates to the radiographic arts. It finds particular application in conjunction with x-ray tubes for computerized tomographic (CT) scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention may also be amenable to other applications.
CT scanners have commonly included a floor-mounted frame assembly which remains stationary during a scan and a rotatable frame assembly. An x-ray tube is mounted to the rotatable frame assembly which rotates around a patient receiving examination region during the scan. Radiation from the x-ray tube traverses the patient receiving region and impinges upon an array of radiation detectors. Using the position of the x-ray tube during each sampling, a tomographic image of one or more slices through the patient is reconstructed.
The x-ray tube typically comprises an x-ray tube insert holded a rotating anode and a stationary cathode and a lead lined housing. The x-ray tube insert is contained within the lead lined housing. Cooling oil is flowed between the x-ray tube insert and the housing. In large, high performance x-ray tubes, the x-ray insert may be a metal shell or frame with a window mounted or brazed thereon for allowing the transmission of x-rays from the x-ray tube. The window may be made of beryllium, titanium or any other x-ray transmitting material. Likewise, the housing defines an xray output window that is in alignment with the beryllium window of the metal frame such that x-rays pass directly through both the beryllium window and the x-ray output window.
During x-ray operation, electrons are emitted from a heated filament in the cathode and accelerated to a focal spot area on the anode. Upon striking the anode, some portion of the electrons, or secondary electrons, are bounced to the surrounding frame and converted into heat. The beryllium window receives the highest intensity of the secondary electron heating because the window is close to the focal spot on the anode. This heat is undesirable and is commonly termed waste heat. One of the persistent problems in CT scanners and other radiographic apparatus is dissipating the waste heat created while generating x-rays.
In order to remove the waste heat, a cooling fluid is often circulated between the housing and the metal frame intert to form a cooling flow path throughout the x-ray tube. For example, cooling oil is drawn through an output aperture located at one end of the housing, circulated through a radiator or heat exchanger and returned to an inlet aperture in the opposite end of the housing. The returned cooled fluid flows axially through the housing toward the outlet aperture, absorbing heat from the x-ray insert.
Removing waste heat in this manner is not always completely effective. More specifically, waste heat removal by merely forcing coolant to flow between the x-ray insert and the housing is particularly ineffective around the x-ray output window. The beryllium window and its environs, being the recipient of the secondary electrons and heat from the closely adjacent focal spot, is preferentially heated. Further, the beryllium window protrudes out from the frame and generally disrupts the flow of coolant around the window preventing optimal cooling. Additionally, the configuration of the x-ray output window on the housing disrupts coolant flow and, by its proximity to the beryllium window, limits the amount of coolant capable of passing over the beryllium window.
When the beryllium window is not sufficiently cooled, the heat can damage the braze joint between the beryllium window and the metal frame insert causing the x-ray tube to fail. Further, the coolant adjacent to the beryllium window may boil and leave a carbon residue on the beryllium window. Such a coating is undesirable as it may degrade the quality of the x-ray image.
The present invention provides a new and improved cooling system for overcoming the above-referenced drawbacks and others.
The present invention relates to the use of a cooling jacket and/or flow baffles around an x-ray insert to provide for the removal of undesirable waste heat from the x-ray tube insert, a beryllium window on the x-ray insert, and the area surrounding the beryllium window.
In accordance with one aspect of the present invention, a CT scanner comprises an x-ray tube mounted on a rotating frame portion. The x-ray tube includes an x-ray insert and a housing. The x-ray insert is mounted in the housing between an anode side cavity and a cathode side cavity with a cooling fluid path surrounding the x-ray insert and running between the anode and cathode side cavities. The x-ray tube has a beryllium window mounted on the x-ray insert, a cooling fluid circulation line, and a cooling fluid return line. The fluid circulation line is in fluid communication with one of the anode side cavity and the cathode side cavity and in fluid communication with a heat exchanger. The fluid return line is in fluid communication with the heat exchanger and in fluid communication with the other one of the anode side cavity and the cathode side cavity. The CT scanner additionally comprises a pump means and a plurality of fins mounted in the cooling fluid circulation line. The pump means circulates the cooling fluid through the heat exchanger, the suction and return lines, and the x-ray tube housing.
In accordance with another aspect of the present invention, an x-ray tube comprises a housing, an x-ray insert, and a plurality of baffles. The housing has an x-ray window and defines a housing cavity therein. The x-ray tube includes a vacuum envelope which holds an anode and a cathode. The vacuum envelope has a beryllium window adjacent the anode. The x-ray insert is mounted in the housing spaced from the housing by an annular fluid path with the beryllium window aligned with the x-ray window. The plurality of baffles is mounted in the flow path for directing cooling fluid toward the beryllium window.
In accordance with another aspect of the present invention, a method of cooling an x-ray tube is provided. A cooling fluid is circulated through an x-ray tube housing. Heat is removed from an x-ray insert disposed within the x-ray tube housing by allowing the circulating cooling fluid to flow adjacent the x-ray insert. Heat is removed from a beryllium window disposed on the x-ray insert by forcing the cooling fluid to converge toward the beryllium window. The forcing is caused by a plurality of baffles disposed angularly relative to the flow direction of the circulating cooling fluid. Heated cooling fluid is removed from the x-ray tube housing. Cooling fluid is cooled and recirculated through the x-ray tube housing.
The advantages of the present invention include the ability to prevent or reduce the risk of thermal damage to the joint between the beryllium window and the metal frame insert.
Another advantage resides in reducing or preventing failure of the x-ray insert due to overheating.
Another advantage of the present invention resides in reducing or preventing carbon build-up on the beryllium window due to overheating of the cooling fluid.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.